1. Field of the Invention
The subject invention relates to a variable-capacity water pump with an impeller construction for use in automotive engines and the like.
2. Description of the Related Art
The cooling mechanism for an internal combustion engine used in an automobile normally comprises a coolant pump, commonly referred to as a water pump, of a centrifugal-type. The most common arrangement utilizes the engine rotation to drive a shaft via a belt connection between a driving pulley (connected to the crankshaft) and a driven pulley. The example shown in FIG. 1 shows a typical water pump 10 with the impeller 20 fastened to a rotating shaft 30 drivable by the pulley 40, which is attached to the engine crankshaft (not shown). The impeller 20 includes a flange 22 having several integral blades or vanes 24 projecting axially toward the inlet path 26. When the pulley 40 rotates, the drive shaft 30 rotates, and the vanes 24 similarly rotate. Coolant enters the passageway 50 and is thrown outward by centrifugal force of the rotating impeller 20 to an outlet port (not shown) via the outlet path 28.
Although this system is simple, it has the disadvantage of supplying a fixed capacity of coolant that is often unnecessarily large. This over-capacity arises because the pump output is sized to deliver a minimum flow amount of coolant at low engine speeds. At higher engine speeds, such as those experienced under normal highway driving conditions, the flow amount becomes excessive because it is directly proportional to engine speed, which is up to an order of magnitude greater. This leads to poor cooling efficiencies and increased power losses.
An alternative arrangement uses an electric motor instead of the engine to drive the impeller. However, this adds weight and cost because extra components are required, and because the capacity of the battery and generator needs to be increased, to supply the extra power needed by the motor.
U.S. Pat. No. 4,094,613, assigned to Sundstrand Corporation, discloses a variable output centrifugal pump utilizing a volute type diffuser in addition to vane diffusers. The variable flow is produced by a telescoping sleeve that closes or opens a main volute diffuser. In this design, a second volute diffuser is always open, so the range of control does not extend to zero flow output. Furthermore, the vane diffusers do not lie in a common plane, which leads to an undesirable increase in the physical volume of the pump.
U.S. Pat. Nos. 4,752,183 and 4,828,455, both assigned to Aisin Seiki Kabushiki Kaisha, propose a variable capacity impeller-type water pump that uses an axially movable thrust shaft and an attached disk or shroud with recesses through which the vanes protrude. A thermostat responds to temperature changes to move the thrust shaft and attached shroud over the vanes to vary the exposed area and therefore the quantity of coolant that flows through the water pump. This design relies on the accuracy of the thermostat, which can be suspect. It also poorly controls flow into the volute, allowing coolant to pass beneath the impeller. Furthermore, it does not allow for varying the pump capacity with the engine rotational speed.
U.S. Pat. No. 5,169,286, also assigned to Aisin Seiki Kabushiki Kaisha, proposes a variable capacity impeller-type water pump that uses coil springs and an attached disk plate or shroud with over-sized recesses through which the impeller vanes protrude with wide clearances. The effective height of the vanes, and hence the cooling capacity of the pump, is determined by the balance of forces exerted by the coil springs and the opposing pressure in the pressurized chamber formed between the impeller flange and the surrounding shroud. Unfortunately, this arrangement has several disadvantages, including unstable flow, unpredictable spring return characteristics, and very small pressure differentials, all of which result in a shroud position that is difficult to determine or control accurately.
The present invention provides a water pump construction with its capacity variable in accordance with an axially movable shroud that exposes a variable amount of impeller vane surface.
According to the present invention, a variable capacity coolant pump includes a pump body having a passage for coolant, a rotatable shaft projecting into the passage, a pump impeller having a flange extending radially outward from the rotatable shaft and a plurality of vanes axially projecting from the flange and configured to cause the flow of coolant through the passage, and a shroud positioned so that it moves from a position whereby the entire vane surfaces of the impeller are surrounded by the shroud, to a position whereby only a portion of the vane surfaces are surrounded, the position determined by either a torsional spring or externally actuated control unit. The external control unit can be integrated with other vehicle management control systems and can operate independently of engine speed, coolant temperature or fluid resistance pressure.